We report two patients with isolated bone marrow non-Hodgkin's lymphoma and we review the additional 23 cases thus far described. Bicytopenia or pancytopenia and an elevated erythrocyte sedimentation rate were universally present. Some 84% of the patients manifested fever of unknown origin (FUO), 64% constitutional symptoms, 48% hepatomegaly, and 52% splenomegaly. Of the variety of therapeutic protocols used, corticosteroids, alone or in combination, appeared to be the most effective. Survival ranged from 1 week to 4.5 years. Early diagnosis would avoid unnecessary work-up in patients with FUO and enable optimization of therapy.